http://webdelprofesor.ula.ve/odontologia/robertramirez/PDF/17.pdf

Resin composite--state of the art.

http://www.fo.usp.br/wp-content/uploads/Restauracao_posteriores.pdf

Longevity of posterior composite restorations: not only a matter of materials

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization-induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors. Fortunately, these materials have been the focus of a great deal of research in recent years with the goal of improving restoration performance by changing the initiation system, monomers, and fillers and their coupling agents, and by developing novel polymerization strategies. Here, we review the general characteristics of the polymerization reaction and recent approaches that have been taken to improve composite restorative performance.

/pdf/recent-advances-and-developments-in-composite-dental-587o691l0q.pdf

Recent Advances and Developments in Composite Dental Restorative Materials

Progress in dimethacrylate-based dental composite technology and curing efficiency

Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach.

Conversion-dependent shrinkage stress and strain in dental resins and composites.

Synthesis and photopolymerization of low shrinkage methacrylate monomers containing bulky substituent groups

Dimethacrylate monomers are used in a wide variety of crosslinked polymer applications, including adhesives, coatings, dental restoratives, and stereolithography. The advantages of rapid curing and good mechanical properties offered by these materials are countered by problems with dimensional changes during polymerization and long-term physical instability resulting from water sorption and loss of residual unreacted monomer. In this work, several examples of hydrophobic monomers based on a dimer acid structure were synthesized, and their monomeric and homopolymer properties were evaluated. The photopolymerization reactivity and conversion were investigated with near-infrared spectroscopy. Studies of the volumetric shrinkage, water sorption, and water contact angle and three-point-bend testing of the homopolymers were also carried out, with the results compared with those of commonly used dimethacrylate monomers. The new monomers produced higher degrees of conversion combined with lower polymerization shrinkage and water sorption values in comparison with conventional monomers. The relatively low crosslink density of dimethacrylates constructed from dimer acid produced polymers with high flexibility and low modulus, as expected; however, changes in the functionality of the group linking the dimer acid core with the methacrylate end groups induced significant property differences. On the basis of the properties demonstrated by the dimer acid monomers and their homopolymers, these new materials appear well suited for applications such as coatings and adhesives.

Dimethacrylate derivatives of dimer acid

Efficient photopolymerization of a potentially expandable monomer is of practical importance for a variety of polymeric applications demanding dimensional stability, particularly if the polymerization process is well controlled based on a detailed investigation of the reaction. In the current study, photoinitiated polymerization kinetics of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane (MPN) either with cationic initiation alone or with combined cationic/free radical initiation was examined using real-time FT-IR. A proposed mechanism based on the simplified propagation steps of the cationic double ring-opening polymerization of MPN was confirmed by both computer modeling and NMR spectroscopic analysis of resulting polymers as well as the experimentally observed apparent activation energy. According to this mechanism, alpha-position attack is the predominant mode for the second ring opening during cationic polymerization of MPN. Further, cationic photopolymerization was performed along with a free radical co-initiator or with exposure to moisture to get an improved understanding of the complex cationic double ring-opening polymerization. As a result, free radical-promoted cationic polymerization helps increase the polymerization rate of MPN while even a trace amount of moisture was found to significantly impact both the reaction kinetics and the polymerization course.

A Mechanistic and Kinetic Study of the Photoinitiated Cationic Double Ring-opening Polymerization of 2-Methylene-7-phenyl-1,4,6,9-tetraoxa-spiro[4.4]nonane.

Incomplete polymerization, volumetric shrinkage, and shrinkage stress are among the primary disadvantages of current resin-based dental composites. Generally, any attempt to increase final double bond conversion only exacerbates polymerization shrinkage and stress. The use of dimer acid-derived dimethacrylate (DADMA) monomers in novel dental resin formulations is examined in this article as a potential means to address these disparate goals. A series of high molecular weight DADMA monomers with different functional groups used to connect the C36 dimer acid core and the methacrylates were formulated with urethane dimethacrylate (UDMA) and/or ethoxylated bisphenol A dimethacrylate (Bis-EMA) at various compositions to manipulate comonomer compatibility and polymeric mechanical properties. Along with reaction kinetics, dynamic polymerization shrinkage and shrinkage stress were assessed. Specific DADMA monomers demonstrated limited miscibility with either Bis-EMA or UDMA. Appropriate ternary resin formulations produced homogeneous monomeric mixtures capable of controlled polymerization-induced phase separation (PIPS) to yield heterogeneous final polymers. Reduced polymerization shrinkage and stress along with higher conversion was observed for DADMA ternary systems compared with a bisphenol A glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) resin control. The PIPS process resulted in a modest volume recovery and stress relaxation in the later stages of polymerization. These results indicate that certain dimer acid-derived dimethacrylates possess the potential to replace TEGDMA as a reactive diluent in dental resins that display a favorable and unique combination of properties.

Junhao Ge

Papers

Conversion-dependent shrinkage stress and strain in dental resins and composites.

Synthesis and photopolymerization of low shrinkage methacrylate monomers containing bulky substituent groups

Dimethacrylate derivatives of dimer acid

A Mechanistic and Kinetic Study of the Photoinitiated Cationic Double Ring-opening Polymerization of 2-Methylene-7-phenyl-1,4,6,9-tetraoxa-spiro[4.4]nonane.

Dental resins based on dimer acid dimethacrylates: a route to high conversion with low polymerization shrinkage.